The present invention relates to the dilemma that confronts digital audio and video content providers as writable storage media inevitably become comparable in cost with read-only media that play in the same devices. At the same time, home computers have become common, if not ubiquitous, and peripheral drives that can transfer information to writable media are increasingly affordable. Naturally, these drives can also read the digital content from read-only media, so even a nominally honest user can be tempted to make unauthorized copies. This scenario is now affecting the digital audio market because CD-R (write-once) discs have become very inexpensive.
Video DVD content is disguised by the Contents Scramble System (CSS). CSS provides that unscrambled digital video outputs are not provided on consumer-market players. Also, unscrambled digital video outputs are not provided on consumer-market DVD-players, and current DVD-ROM drives that play video DVD discs output scrambled content to a separate licensed software or hardware decoder. But, CSS alone cannot prevent a consumer player from playing sector-by-sector copies of protected content on writable discs with a compatible format. The details of CSS system are not supposed to be public knowledge, but a general description was given by Michael Moradzadeh of Intel in “Licensing Requirements for the CSS DVD Copy Protection Method”, Intel, 1997.
To inhibit playback of unauthorized sector-by-sector copies, a group of companies known as the 4C Entity proposed “Content Protection for Recordable Media” (CPRM) which is available from 4C License Entity LLC, 225B Cochrane Circle, Morgan Hill, Calif. 95037. CPRM uses a “Protected Media Identifier,” when scrambling and unscrambling content. This ensures that protected content copied directly from one disc to another cannot be played back because the identifications would not match. However, CPRM does not prevent scrambled content from being copied onto a writable disc sector-by-sector, which could be the first step in illegally voiding the copy protection of a digital disc.
A sector-by-sector copy of a CPRM disc would only lack the media identifier of the original disc, which an adversary could read and try to provide during playback from an unauthorized copy. This might require only limited reverse engineering of CPRM's decryption algorithm in a software implementation on a personal computer.
Copy protection generally endangers backward compatibility of future players. Even if copy protection were to be abandoned however, the rapid evolution of optical disc technology threatens to make old discs unreadable in future players.
In spite of the teachings of the above mentioned, there is still a significant need for a copy-resistant read-only digital optical disc having encrypted digital data.
It is therefore a principal object of the present invention to provide a variable disc format that players can read but can nevertheless be changed as necessary to make sector-by-sector copying onto writable discs infeasible.
It is still another object of the present invention to provide variable software algorithms for encrypting a digital work which can be updated or even changed completely while still maintaining playability in existing players.
It is yet another object of the present invention to provide future players or drives a method of adapting to antiquated discs using information provided on the discs themselves.